Aqueous beta cobaltous hydroxide and method for making

ABSTRACT

Beta cobaltous hydroxide is synthesized by decomposing the complex formed between cobaltous ions and a suitable complexing agent under hydrothermal conditions. Cobaltous ion and complexing agent are combined in an aqueous medium, wherein the molar ratio of the cobaltous ion to the complexing agent is about one or more. Hydroxide ion is added, wherein the molar ratio of hydroxide ion to cobaltous ion is more than about 2. The resulting admixture is heated under hydrothermal conditions for precipitating beta cobaltous hydroxide. The method provides improved control over the size and shape of the beta cobaltous hydroxide reaction product. The beta cobaltous hydroxide can be reduced to form magnetic particles of cobalt metal.

This is a continuation of application No. 07/771,488 filed Oct. 4, 1991,now abandoned, which is a division of application No. 07/447,668 filedDec. 8, 1989, now issued as U.S. Pat. No. 5,057,299.

FIELD OF THE INVENTION

This invention relates to the synthesis of beta cobaltous hydroxideunder hydrothermal conditions. This invention also relates to a novel,aqueous admixture suitable for hydrothermal treatment to prepare betacobaltous hydroxide.

BACKGROUND OF THE INVENTION

The trend in the magnetic recording industry is towards higher densityrecording. Higher density recording requires materials with improvedsignal output at shorter wavelengths. Higher density recording alsorequires materials in which self-demagnetization can be minimized asmuch as possible.

One material that shows great potential for high density recordingapplications is cobalt metal. A cobalt metal particle can have aplatelet-shape and a close-packed, hexagonal crystallographic structure.Cobalt metal particles with a close-packed, hexagonal, platelet shapehave an easy axis of magnetization that is perpendicular to the plane ofthe particle. Such cobalt metal particles have high saturationmagnetization, over 100 emu/g, and coercivities of up to 2000 Oe.

Cobalt metal particles suitable for magnetic recording are obtained bythe reduction of pink, hexagonal, platelet-shaped beta cobaltoushydroxide. Various methods for making the beta cobaltous hydroxideprecursor are known in the art. In one typical method, beta cobaltoushydroxide is made by reacting a cobaltous salt in an alkaline solutionto form a precipitate of beta cobaltous hydroxide. This directprecipitation method is described in each of the Japanese publicationsJP54-75597, JA60-263328, and JP61-163123.

Unfortunately, the direct precipitation method provides insufficientcontrol for adjusting the average particle size of the beta cobaltoushydroxide reaction product beyond a very limited range. What was neededin the art was a method of making beta cobaltous hydroxide in which adesired average particle size could be easily obtained over a relativelybroader size range, while at the same time maintaining uniform particleshape and a narrow particle size distribution.

SUMMARY OF THE INVENTION

The present invention relates to an improved method for making betacobaltous hydroxide. It has been discovered that beta cobaltoushydroxide can be synthesized by decomposing the complex formed betweencobaltous ions and a suitable complexing agent under hydrothermalconditions in basic solution. The present invention provides asignificantly improved method of making beta cobaltous hydroxide inwhich a desired average particle size can be easily obtained over arelatively broad size range, while at the same time maintaininghexagonal, platelet particle shape and a narrow particle sizedistribution.

The beta cobaltous hydroxide according to the present invention can bereduced to form magnetic particles of cobalt metal. The magneticparticles of cobalt metal thus formed have an electromagneticperformance suitable for magnetic recording applications, such as highdensity magnetic recording.

One aspect of the present invention concerns a novel composition that isuseful for the hydrothermal synthesis of beta cobaltous hydroxide. Thecomposition is an admixture of ingredients comprising a cobaltous ion, asuitable complexing agent, a hydroxide ion, and an aqueous medium.

The cobaltous ion is derived from a cobaltous salt which may contain anyof a variety of counter ions. The concentration of cobaltous ion in theadmixture is not critical, so long as the concentration of the cobaltoussalt is less than its saturation concentration prior to the addition ofthe hydroxide ion, and so long as the molar ratio of the cobaltous ionto the other ingredients is within the ranges discussed hereinafter. Itis desirable, however, that sufficient cobaltous ion is present toprovide desired yields.

The complexing agent has at least one functional group, and preferablytwo functional groups, capable of acting as a Lewis base towards thecobaltous ion. Additionally, the complexing agent is capable of forminga water-soluble complex with the cobaltous ion. It is also believed thatthe complexing agent stabilizes alpha cobaltous hydroxide in basicsolution at about room temperature. The molar ratio of the cobaltous ionto the complexing agent in admixture is about one or more.

The hydroxide ion is derived from a hydroxide base which may contain anyof a variety of counter ions. The molar ratio of the hydroxide ion tothe cobaltous ion in admixture is at about 2 or more.

The aqueous medium is preferably deionized water having a conductivityof about 50 μmhos or less.

In another aspect, the present invention concerns a novel, hydrothermalmethod for making aqueous, platelet-shaped, hexagonal beta cobaltoushydroxide. Hydrothermal conditions means that the reaction takes placein an aqueous reaction medium at an elevated pressure within thespecified temperature range. The elevated pressure is not critical aslong as the pressure is sufficient to constrain the aqueous reactionmedium to the liquid phase. Batch and continuous methods are within thescope of the invention.

The method of the present invention comprises combining a cobaltous ion,a suitable complexing agent, and an aqueous medium to form an aqueoussolution. At least about two moles of a hydroxide ion are added to theaqueous solution for each mole of cobaltous ion, thereby forming anadmixture of ingredients comprising the cobaltous ion, the complexingagent, the hydroxide ion, and the aqueous medium. After adding thehydroxide ion, the admixture is heated under hydrothermal conditions toa reaction temperature of from about 100° C. to about 268° C. Theadmixture is maintained under hydrothermal conditions at the reactiontemperature for a time sufficient to precipitate the cobaltous ion asbeta cobaltous hydroxide.

In the described method, the complexing agent, the molar ratio of thecobaltous ion to the complexing agent, the molar ratio of the hydroxideion to the cobaltous ion, the aqueous medium, and the concentration ofthe cobaltous ion in admixture are as defined above.

The present invention provides excellent control over the averageparticle size of the beta cobaltous hydroxide reaction product. Startingwith the same admixture, a desired average particle size ranging fromabout 0.05 μm to about 0.5 μm or more can be easily obtained merely byadjusting the reaction temperature. Further control is achieved byadjusting the concentration of starting materials in the admixture or byadjusting the reaction time.

Practical tests have shown that such control is not provided by thedirect precipitation method. Although average particle size generallyincreases with higher reaction temperature using the directprecipitation method, it has been found that the average particle sizevaries within a relatively narrow range between the lowest availabletemperature (0° C.) and the highest available temperature (100° C.).Temperatures outside this range are not available using the directprecipitation method, since water freezes below 0° C. and vaporizesabove 100° C.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described above, beta cobaltous hydroxide can be synthesized bydecomposing the complex formed between the cobaltous ion and acomplexing agent under hydrothermal conditions in basic solution. Thecobaltous ion is derived from a cobaltous salt which may contain any ofa variety of counter ions. Examples of suitable counter ions include,but are not limited to, sulfate, or nitrate. It has been found thatvarying the counter ion for the cobaltous salt has a minimal effect uponthe particle morphology or size of the beta cobaltous hydroxide reactionproduct.

The concentration of the cobaltous ion in the aqueous solution is notcritical so long as this concentration is less than the saturationconcentration of the cobaltous salt prior to the addition of thehydroxide ion and so long as the desired relative proportions ofingredients are maintained. If the concentration is too low, however,the yield of beta cobaltous hydroxide may be too low to be efficient oreconomical for commercial applications. On the other hand, if theconcentration is too high, then the solution may be too sensitive tochanges in processing parameters, such as temperature, concentrations ofindividual components, and the like, resulting in undesirableprecipitation and fouling of the processing equipment.

Complexing agents useful in the present invention have at least onefunctional group capable of acting as a Lewis base towards the cobaltousion. In other words, the complexing agent is capable of acting as aligand in which at least one functional group can complex at acoordination site relative to the cobaltous ion. Preferably, thecomplexing agent has two functional groups, each functional groupcapable of acting as a Lewis base towards the cobaltous ion at the sametime as the other functional group. Additionally, the complexing agentforms a water-soluble complex with the cobaltous ion.

Examples of suitable complexing agents include amides or a salt thereofsuch as urea and acetamide; amines or salts thereof such asethylenediaminetetraacetic acid, diethanolamine and triethanolamine;sugars such as glucose, sucrose, lactose, maltose and mannitol;α-hydroxy carboxylic acids or a salt thereof such as gluconic acid,tartronic acid, saccharic acid, tartaric acid, lactic acid, malic acidand glycolic acid; α-amino carboxylic acid or a salt thereof such asaspartic acid and glutamic acid; other carboxylic acids or a saltthereof such as propanoic acid, adipic acid, malonic acid, acetic acid,citric acid and ascorbic acid.

Preferably, the complexing agent is a sugar such as glucose, lactose,maltose, and sucrose; or an α-hydroxy carboxylic acid or a salt thereofsuch as tartronic acid, saccharic acid, tartaric acid; or tartrate salt.

Most preferably, the complexing agent is a tartrate salt. Examples ofsuitable tartrate salts include those tartrate salts having aneutralizing number of counter ions selected from the group consistingof sodium, potassium, ammonium, and lithium. Combinations of thesecounter ions are also within the scope of the invention. For example,potassium sodium tartrate is a suitable tartrate salt. Use of lithium isbest for controlling the average particle size and maintaining thehexagonal, platelet shape of the beta cobaltous hydroxide particles.Even though lithium tartrate has such an advantage, the other tartratesalts, such as sodium potassium tartrate, are more economical to use.Additionally, use of these other tartrate salts will still provide betacobaltous hydroxide particles that can be reduced to cobalt metalparticles suitable for magnetic recording applications.

According to the invention, the molar ratio of cobaltous salt to thecomplexing agent is about one or more. Preferably, the molar ratio ofthe cobaltous ion to the complexing agent is from about one to about 20.Most preferably, the molar ratio is from about two to about 10.

Particle shape and size are highly dependent upon this molar ratio. Whenthe molar ratio is about one or more, a substantial majority of the betacobaltous hydroxide reaction product comprises platelet-shaped,hexagonal particles. When the molar ratio is varied from about one toabout 8, it has been found that the variation of the molar ratio withinthis range has only a minimal effect upon average particle size. Whenthe molar ratio is greater than about 8, however, it has been found thataverage particle size increases as this molar ratio is increased. On theother hand, when the molar ratio is less than about one, the averageparticle size of the beta cobaltous hydroxide reaction product is harderto control, and substantial portions of the reaction product may nothave a hexagonal, platelet shape.

Although not wishing to be bound by any particular theory, a possiblerationale to explain the function of the complexing agent can besuggested. In basic solution, cobaltous hydroxide may exist as the alpha(blue) phase or the beta (pink) phase. If the alpha phase is present insolution, a blue precipitate will be seen. If the beta phase is presentin solution, a pink precipitate will be seen. If both phases are presentin a solution, a lavender precipitate will be seen.

In the absence of a complexing agent, the alpha phase is unstable in anaqueous, basic solution, and will dissolve and precipitate as the morestable phase, beta cobaltous hydroxide. Without a complexing agent, onlyminimal control over the size and shape of this precipitate is possible.

In the presence of a complexing agent such as potassium sodium tartrate,the chemistry of the aqueous, basic solution is different. Thesignificance of this difference in chemistry substantially depends uponthe molar ratio of the cobaltous ion to the complexing agent. It is animportant feature of the invention that this ratio is one or more. Whenthe ratio is one or more, the cobaltous ion is in excess. Under theseconditions, only a portion of the cobaltous ion forms a water solublecomplex with the complexing agent. The excess cobaltous ion in admixturesurprisingly reacts to form a blue or a lavender precipitate, indicatingthe presence of the alpha phase. Hence, when the molar ratio ofcobaltous salt to the complexing agent is about one or more, it isbelieved that the complexing agent not only forms a water solublecomplex with the cobaltous ion, but also stabilizes the blue alpha phasein basic solution at room temperature. This is a significant feature ofthe invention in that the blue alpha cobaltous hydroxide apparentlyfunctions as seed particles for precipitating beta cobaltous hydroxidecrystals under further hydrothermal treatment.

When the ratio of cobaltous ion to the complexing agent is less thanone, there is a molar excess of the complexing agent. Under theseconditions, most of the cobaltous ion is in the form of a water solublecomplex. No precipitate forms, and the solution is transparent. Uponhydrothermal treatment of the transparent solution, the cobaltouscomplex decomposes and a precipitate forms. However, substantialportions of this precipitate may not be hexagonal or platelet-shapedparticles.

The aqueous medium useful in the present invention preferably isdeionized water having a conductivity of 50 μmhos or less, and morepreferably 10 μmhos or less. Optionally, the aqueous medium may alsocomprise a surfactant. A surfactant is added to decrease the viscosityof the aqueous medium. Examples of suitable surfactants includepolymethacrylate, polyacrylate, polyethylene glycol, and polyvinylalcohol.

At least two moles of hydroxide ion are added to the aqueous solutionfor each mole of the cobaltous ion. This is the minimum molar rationeeded to satisfy the stoichiometric relationship between the cobaltousand the hydroxide species in the cobaltous hydroxide reaction product.When the molar ratio of the hydroxide ion to the cobaltous ion is about2 or more, platelet-form, hexagonal beta cobaltous hydroxide particlesprecipitate upon hydrothermal treatment. When this molar ratio is lessthan about 2, the hydrothermal reaction product is not crystalline, andthe cobaltous hydroxide product may not have a hexagonal, plateletshape.

Preferably, the molar ratio of the hydroxide ion to the cobaltous ion isfrom about 3 to about 20. when the ratio is more than 20, the presenceof the excess hydroxide ion requires extensive washing after synthesisin order to lower the conductivity of the product slurry prior to dryingthe product.

The concentration of the hydroxide base also affects the percent carbonimpurity present in the beta phase reaction product. The carbon impurityis believed to come from the complexing agent. When reacted with acobaltous ion in aqueous solution, the complexing agent bonds to thecobaltous ion at one or more coordination sites, thereby forming awater-soluble complex. The hydroxide base tends to displace thecomplexing agent at the coordination sites when treated hydrothermallyto form beta cobaltous hydroxide precipitate. Any non-displacedcomplexing agent, or carbon impurity, gets incorporated into the crystallattice of the precipitate, resulting in a lattice defect. It isdesirable to minimize such defects by minimizing the percent carbonimpurity present in the beta phase reaction product. It has been foundthat the percent carbon impurity in the beta cobaltous hydroxideparticles decreases when higher concentrations of the hydroxide base areused in the present invention.

The magnetic properties of the cobalt metal particles obtained byreduction of the beta cobaltous hydroxide particles also depend upon theconcentration of the hydroxide base. It has been found that theseproperties improve when higher concentrations of hydroxide base are usedin the present invention.

Various cations can be used as counter ions for the hydroxide base.Typically, the cation is an alkali metal cation, such as lithium,sodium, or potassium. Lithium is preferred in that use of lithiumhydroxide provides excellent control over the average particle size ofthe beta phase reaction product. Even so, the other alkali metalhydroxides, such as sodium hydroxide, are more economical to use, andtheir use will still provide beta cobaltous hydroxide particles thatreduce to cobalt metal particles suitable for magnetic recordingapplications. The hydroxide ion may also be derived from other hydroxidebases such as calcium hydroxide and magnesium hydroxide.

After all of the components have been added, the admixture is heatedunder hydrothermal conditions to a reaction temperature of from about100° C. to about 268° C. The reaction temperature must be at least 100°C. to get a crystalline reaction product. Above about 268° C., thereaction product is cobaltous oxide rather than the desired betacobaltous hydroxide.

The average size of the beta cobaltous hydroxide particles increaseswhen synthesized at the higher reaction temperatures. It has also beenfound that the use of a higher reaction temperature leads to a betacobaltous hydroxide reaction product that reduces more easily to formcobalt metal particles having higher squareness and remanentmagnetization, and a narrower switching field distribution.

The composition is maintained under hydrothermal conditions at thereaction temperature for a time sufficient to precipitate the cobaltousion as beta cobaltous hydroxide. A longer residence time in thehydrothermal reactor provides a beta phase reaction product with largeraverage particle size at a given temperature. Under hydrothermalconditions, the cobaltous complex decomposes in the presence of thehydroxide base, providing for the precipitation of the cobaltous ion asbeta cobaltous hydroxide. It is believed that the blue alpha cobaltoushydroxide particles, which are converted into pink, platelet-shaped,hexagonal beta cobaltous hydroxide in the hydrothermal reactor, serve asseeds, or nucleation sites, for growth of the beta phase crystals.

Generally, in the method of the invention, either batch or continuoushydrothermal reaction equipment can be used with appropriate alterationof reaction time and temperature.

Analysis of powder x-ray diffraction patterns suggest that betacobaltous hydroxide particles prepared at the higher reactiontemperatures and base concentrations are more crystalline. Relativedegrees of crystallinity can be determined by measuring the widths ofthe diffraction peaks for the beta cobaltous hydroxide particles.Crystalline material will produce sharper diffraction peaks than amaterial that is less crystalline. However, in the case of betacobaltous hydroxide particles, the interpretation of the diffractiondata is complicated by the fact that particle sizes less than 0.1 μmalso cause the peaks to broaden. Some of the particles subjected tox-ray diffraction analysis were in the size range where both crystallinedefects and particle size could yield broad diffraction peaks.

The invention will be further described by reference to the followingexamples.

EXAMPLE 1

Platelet-shaped, hexagonal beta cobaltous hydroxide particles wereprepared in a batch hydrothermal reactor. The batch reactor was a 2liter, stainless steel Parr reactor having a Teflon liner.

A cobaltous solution was prepared by dissolving 87 grams of cobaltousnitrate hexahydrate and 85 grams of potassium sodium tartrate in 800 mlof deionized water. The ratio of cobaltous ion to tartrate was one. Abasic solution was prepared by dissolving 120 grams of NaOH in 200 ml ofdeionized water. The basic solution was added to the cobaltous solution.The concentration of NaOH was 3 moles per liter and the molar ratio ofhydroxide ion to cobaltous ion was 10. No precipitate of pink, betacobaltous hydroxide formed at room temperature. Instead, the resultingadmixture was blue and contained colloidal particles of alpha cobaltoushydroxide.

The admixture was placed into the reactor vessel. The reactor contentswere heated to about 200° C. over 70 minutes. During heating, thereactor contents were stirred at a rate of 600 rpm. The temperature wasmaintained at 200° C. for 30 minutes. After heating, the reactorcontents were cooled to about room temperature by running tap water overthe reactor. The cooled reactor contents comprised a pink slurry.

After cooling, the pink slurry was transferred to a 20 liter Pyrexwashing vessel. The pink slurry in the washing vessel was washed withdeionized water until the wash water had a conductivity of less than 50μmhos. The pink slurry was passed through a filter, and pink particleswere collected on the filter. The collected particles were washed twicewith acetone and dried at room temperature.

Transmission electron micrographs revealed that the material wasplatelet-shaped, hexagonal beta cobaltous hydroxide particles having anaverage size of about 0.50 μm.

EXAMPLE 2

Platelet-shaped, hexagonal beta cobaltous hydroxide particles wereprepared in a continuous hydrothermal reactor.

About 9000 grams of a first aqueous solution comprising about 8% byweight cobaltous in deionized water was mixed with a second aqueoussolution comprising 862 grams of sodium potassium tartrate tetrahydratein 11430 grams of deionized water. An additional 12330 grams ofdeionized water was added to the aqueous mixture. After adding theadditional water, 4200 grams of a 50% by weight aqueous solution of NaOHwas added to the mixture, thereby forming an admixture comprising thecobaltous salt, the tartrate salt, the hydroxide base, and the deionizedwater. In this admixture, the molar ratio of cobaltous salt to thetartrate salt was 4, the concentration of the caustic hydroxide was 1.5moles per liter, and the molar ratio of hydroxide ion to cobaltous ionwas 5.

The admixture was pumped through a continuous hydrothermal reactor. Thereactor was a 160 cubic centimeter coil immersed in an oil bathmaintained at 250° C. The flow rate of the admixture through the reactorwas 100 cm³ /min. The product stream emerging from the reactor compriseda pink slurry. The slurry was washed until the conductivity of the washwater was less than about 50 μmhos. A sample of the washed slurry wascollected on a filter paper and dried at room temperature. After drying,the residue on the filter paper was a pink, particulate product.

Transmission electron micrographs demonstrated that the particles wereplatelet-shaped, hexagonal particles having an average size of 0.1 μm.X-ray diffraction confirmed that the material was beta cobaltoushydroxide.

EXAMPLE 3

This example is intended to show that the particles of beta cobaltoushydroxide made according to the present invention can be reduced tocobalt metal particles by further processing.

A slurry emerging from the continuous hydrothermal reactor scheme ofExample 2 was washed with deionized water until the conductivity of thewash water was less than 50 μmhos. The washed slurry weighed 3049 g andcomprised 100 g of beta cobaltous hydroxide. Next, an anti-sinteringagent was adsorbed onto the beta cobaltous hydroxide. To accomplishthis, the washed slurry was homomixed with 62.5 ml of a NaOH solutionprepared by dissolving 18 grams NaOH in 250 ml of deionized water and62.5 ml of a solution prepared by dissolving 56 grams Al(NO₃)₃.9H₂ O in250 ml of deionized water. The slurry was washed with deionized wateruntil the conductivity of the wash water was less than about 50 μmhos.The washed particles were collected on filter paper and air dried atroom temperature. The dried particles were crushed to pass through a No.10 mesh screen.

About 50 grams of the crushed particles of beta cobaltous hydroxide werethen reduced to cobalt metal particles. To accomplish this, the crushedparticles were placed into a 2 inch by 16 inch fluidized bed made fromquartz and pre-heated to 450° C. in a nitrogen purge entering the baseof the fluidized bed. The flow rate of the nitrogen purge was 30 cubicfeet per hour. The contents of the fluidized bed were maintained at atemperature of about 450° C. for 30 minutes. As a result of thepre-heating, the beta cobaltous hydroxide was dehydrated to cobaltousoxide. The purpose of the pre-heating was to minimize crystallographicdefects in the particles prior to reduction. After pre-heating, thetemperature was lowered to 400° C. and the purge gas was changed fromnitrogen to hydrogen for conversion to cobalt metal. The flow rate ofthe hydrogen purge was 80 cubic feet per hour. These reducing conditionswere maintained for 30 minutes. After this time, the contents of thefluidized bed were cooled to room temperature under a nitrogen purge of50 cubic feet per hour. After cooling, the reduction product wastransferred to a nitrogen-purged glove box for further analysis.

X-ray diffraction confirmed that the reduction product was predominantlycobalt metal particles. The magnetic moment of the cobalt metal productwas 131 emu/g with a squareness of 0.69. The coercivity was 840 Oe. Theswitching field distribution was 0.91 and the magnetic remanence, Br,was 2020 Gauss.

EXAMPLE 4

Electromagnetic performance of cobalt metal particles prepared by themethod of Example 3 was evaluated by grinding the cobalt metal particleswith 7% by weight of tridecyl polyethyleneoxide phosphate estersurfactant such that the solids were 80% by weight in toluene. Morespecifically, 16.0 grams of the cobalt metal, 1.1 grams of tridecylpolyethyleneoxide phosphate ester surfactant and 4.3 grams of toluenewere mixed and ground with 200 grams of a stainless steel media in amill for 60 minutes. After grinding, a polymeric binder and a sufficientamount of methyl ethyl ketone were added such that the solids were 50%by weight. To accomplish this, 10.5 grams of the binder and 10.3 gramsof methyl ethyl ketone were added to the mill. The binder was preparedby mixing 570 grams of vinyl chloride vinyl acetate resin (VYHH vinylresin from Union Carbide Corporation), 187.5 grams of dioctyl phthalate,and 1222 grams of methyl ethyl ketone. After adding the binder and themethyl ethyl ketone, the mixture was milled for about an additional 15minutes to form a cobalt metal dispersion for electromagnetic testing.

EXAMPLE 5

Samples of beta cobaltous hydroxide were prepared in a continuoushydrothermal reactor in order to determine the size of the betacobaltous hydroxide particles as a function of temperature. For samples1-5, the flow rate of reactants through the reactor was 100 cm³ /min.The concentration of NaOH was 2M. The cobaltous ion to tartrate molarratio was held constant at 2. For samples 6-10, the flow rate wasdecreased to 50 cm³ /min. For each sample, size was measured in terms ofthe nitrogen specific surface area of the particles. A larger nitrogenspecific surface area corresponds to a smaller particle. The results areshown in Table 1:

                  TABLE 1                                                         ______________________________________                                                                 Nitrogen                                                                      Specific Surface                                     Sample     Temperature (°C.)                                                                    Area (m.sup.2 /g)                                    ______________________________________                                        1          175           96                                                   2          200           75                                                   3          225           52                                                   4          250           26                                                   5          275           13                                                   6          175           85                                                   7          200           63                                                   8          225           39                                                   9          250           18                                                   10         275           13                                                   ______________________________________                                    

These results show that particle size increases at higher temperatures.These results also show that increasing the residence time by decreasingthe flow rate from 100 cm³ /min to 50 cm³ /min slightly increased theaverage particle size at a given temperature.

Electron micrographs revealed that the particles were hexagonal from175° C. to 250° C., but were not hexagonal at 275° C. Powder x-raydiffractions confirmed that the particles produced at 250° C. and belowwere beta cobaltous hydroxide, while the particles produced at 275° C.were cobaltous oxide.

Other embodiments of this invention will be apparent to those skilled inthe art from a consideration of this specification or practice of theinvention disclosed herein. Various omissions, modifications, andchanges to the principles described herein may be made by one skilled inthe art without departing from the true scope and spirit of theinvention which is indicated by the following claims.

What is claimed is:
 1. A composition that is an admixture of ingredientscomprising blue cobaltous hydroxide and a complex of cobaltous ion and acomplexing agent, said composition being formed by combining thefollowing materials:a) the cobaltous ion; b) the complexing agentwherein the complexing agent is selected from the group consisting of anα-hydroxy carboxylic acid; a salt of an α-hydroxy carboxylic acid; anα-amino carboxylic acid; a salt of an α-amino carboxylic acid; andmixtures thereof, and wherein the cobaltous ion is in excess relative tothe complexing agent; c) a sufficient amount of hydroxide ion such thatthe molar ratio of the hydroxide ion to the cobaltous ion is more thanabout 2; and d) an aqueous medium.
 2. The composition of claim 1,wherein the complexing agent is a tartrate salt.
 3. The composition ofclaim 2, wherein the tartrate salt is selected from the group consistingof sodium tartrate, potassium tartrate, lithium tartrate, and potassiumsodium tartrate.